It is never easy to tell one deermouse from another. Black-wristed Deermice are dusky-brown all the way to the base of their toes. Their fur is long and soft. They are smaller than three species that occur in the same area, larger than one, and females have two pairs of nipples on the abdomen; the others have an additional pair on the chest. A fifth species can only be distinguished by inspecting their teeth and skulls.

Black-wristed Deermice live in cool, wet mountain forests. They shelter in big, exposed tree roots, but have not been seen climbing trees. Runways among the roots hold piles of partly-eaten acorns and other seeds. They probably breed all year, but breeding peaks from March to July. Females have litters of 1 to 3 after a month-long gestation period. The young mice's eyes open at about 3 weeks and they are weaned soon thereafter. By 6 or 7 weeks, they are about half the weight of adults. In captivity, males help with the parenting, maintaining the nest and grooming the young. This suggests that in the wild, pairs may be monogamous.